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Limbo Walkthrough Chapter 35
Press the gravity switch.
Eventually a little tram will come gliding on the cable. It's going to be moving pretty fast.
You want to press the gravity switch before the tram gets there. You don't even want the tram to hit the bumper at the end of the cable.
If done correctly, you will be able to run and jump to the rope under the tram.
Let go of the tram rope, prior to getting impailed on the spikes.
Slide down the slope.
Jump and press the gravity box while you are in the air.